Synchronous detection for photoconductive detectors

• US 6,064,054 A
• Filed: 04/27/1998
• Issued: 05/16/2000
• Est. Priority Date: 08/21/1995
• Status: Expired due to Fees

• Current Assignee: Dominion Assets LLC
• Original Assignee: Diasense Inc.
• Inventors: Wiggins, Richard L., Waczynski, Augustyn
• Primary Examiner(s): Lee, John R
• Application Number:
  US09/011,291
• Time in Patent Office: 750 Days
• Field of Search: 250/214 R, 250/214 LA, 250/214 C, 250/208.1, 250/208.2, 250/206, 250/336.1, 250/338.1, 250/338.4, 250/339.01, 250/339.02, 250/341.5 , 250/214 B, 250/205
• US Class Current: 250/214.00R
• CPC Class Codes: G01J 5/0805 Means for chopping radiation
• CPC Class Codes: G01J 5/30 Electrical features thereof
• CPC Class Codes: H04B 10/6911 Photodiode bias control, e.g. for compensating temperature variations
• CPC Class Codes: H04N 23/20 for generating image signals from infrared radiation only
• CPC Class Codes: H04N 25/65 applied to reset noise, e.g. KTC noise related to CMOS structures by techniques other than CDS
• CPC Class Codes: H04N 5/33 Transforming infrared radiation cameras or camera modules for generating image signals from infrared radiation H04N23/20; circuitry of SSIS for transforming infrared radiation into image signals H04N25/20

Abstract

Disclosed is a radiation detector which includes a photoconductive detector and a modulator which modulates radiation passing to the photoconductive detector from a radiation source. An AC bias source is connected to the photoconductive detector and provides at least two levels of bias thereto. The modulator supplies synchronization signals to the AC bias source such that the level of bias supplied to the photoconductive detector is synchronized to the modulation of the radiation by the modulator. An integrator is connected to and receives an output signal generated by the photoconductive detector.

Claims

1. A method of biasing a photoconductive detector to obtain synchronous detection, said method comprising the steps of:

a) modulating radiation passing from a radiation source to a photoconductive detector,

b) applying an AC bias to the photoconductive detector in a manner which is synchronized with the modulation of the radiation passing to the photoconductive detector, and

c) integrating an output signal generated by the photoconductive detector over a predetermined time period.

2. The method of claim 1 wherein the modulation of the radiation includes at least on and off modulation.

3. The method of claim 1 wherein the modulation of the radiation is a square wave modulation.

4. The method of claim 2 wherein the AC bias includes a first DC voltage of a particular polarity which is applied to the photoconductive detector when radiation is passing to the photoconductive detector and wherein the AC bias includes a second DC voltage at a polarity opposite that of the first DC voltage which is applied to the photoconductive detector when no radiation is passing to the photoconductive detector.

5. The method of claim 4 wherein the AC bias is at a zero volt level when the radiation passing to the photoconductive detector is present but is less than a particular level of radiation.

6. The method of claim 4 wherein the magnitude and duration of the first and second DC voltages are selected such that integration of the output signal generated by the photoconductive detector is zero when no radiation is passing to the photoconductive detector.

7. A radiation detector comprising a photoconductive detector, a modulator which modulates radiation passing to said photoconductive detector from a radiation source, an AC bias source connected to the photoconductive detector and providing at least two levels of bias thereto, with the modulator supplying synchronization signals to the AC bias source such that the level of bias supplied to the photoconductive detector is synchronized to the modulation of the radiation by the modulator, and an integrator connected to and receiving an output signal generated by the photoconductive detector.

8. The radiation detector of claim 7 wherein the modulator provides at least on and off modulation of the radiation.

9. The radiation detector of claim 8 wherein the modulator provides square wave modulation of the radiation.

10. The radiation detector of claim 8 wherein the modulator is a rotating slotted disk.

11. The radiation detector of claim 8 wherein the AC bias source provides, under control of the synchronization signals, a first DC bias voltage at a particular polarity to the photoconductive detector when the modulator passes radiation to the photoconductive detector and wherein the AC bias source provides a second DC bias voltage at the opposite polarity to the photoconductive detector when the modulator passes no radiation to the photoconductive detector.

12. The radiation detector of claim 11 wherein the AC bias source additionally provides, under the control of the synchronization signals, an AC bias to the photoconductive detector at zero volts when the modulator passes radiation to the photoconductive detector at less than a predetermined level and greater than no radiation.

13. The radiation detector of claim 7 wherein the integrator is a charge integrator including an amplifier and a charge capacitor.

14. The radiation detector of claim 13 further including a noise reduction circuit attached to an output of the charge integrator and configured to eliminate kTC noise generated by the charge capacitor.

15. A radiation detector comprising a plurality of separate photoconductive detector elements arranged on a substrate in a linear array, a modulator which modulates radiation passing to each detector element from a radiation source, an AC bias source connected to each detector element and providing at least two levels of bias thereto, with the modulator supplying synchronization signals to the AC bias source such that the level of bias supplied to each detector element is synchronized to the modulation of the radiation by the modulator, and a separate integrator connected to and receiving an output signal generated by each detector element.

16. The radiation detector of claim 15 wherein the modulator provides at least on and off modulation of the radiation.

17. The radiation detector of claim 16 wherein the modulator provides square wave modulation of the radiation.

18. The radiation detector of claim 16 wherein the AC bias source provides, under control of the synchronization signals, a first DC bias voltage at a particular polarity to the detector elements when the modulator passes radiation to the detector elements and wherein the AC bias source provides a second DC bias voltage at the opposite polarity to the detector elements when the modulator passes no radiation to the detector elements.

19. The radiation detector of claim 18 wherein the AC bias source additionally provides, under the control of the synchronization signals, an AC bias to the detector elements at zero volts when the modulator passes radiation to the detector elements at less than a predetermined level and greater than no radiation.

20. The radiation detector of claim 15 wherein the integrator is a charge integrator including an amplifier and a charge capacitor.